1. Field of the Invention
The present invention relates to curable resin systems.
2. Discussion of background technology
Monomers based on vinyl ethers have the following formula: ##STR1## where R is an organic moiety. These compounds will polymerize with cationic initiators (acid catalysis) and will cure fairly rapidly; however, for film application, properties tend to be sub-standard due to the absence of polymeric oligomers which improve the tensile elastic characteristics of the coating. Epoxy, epoxy acrylate and urethane acrylate oligomers normally used in ultra-violet radiation cured coatings do not react well with vinyl ethers.
U.S. Pat. No. 4,775,732 discloses vinyl ether terminated ester and urethane resins from bis(hydroxyalkyl)cycloalkanes which cure by radiation-induced cationic polymerization. U.S. Pat. No. 4,749,807 discloses vinyl ester oligomers, and U.S. Pat. No. 4,751,273 discloses vinyl ether terminated urethane resins. EP-A-0 322 808 discloses a liquid radiation curable composition comprising an unsaturated polyester component and a non-polymerized, co-curable vinyl ether component containing at least two vinyl ether groups.
Cationic initiators are based on onium salts which, when exposed to ultra-violet radiation, decompose to a free radical and a powerful friedel-crafts acid. It is the acid that initiates and promotes cure. Cationic initiators were designed initially to be used with epoxy-type oligomers and monomers. A number of aliphatic based oligomers and resins cure with these types of initiators, and although excellent film and adhesion properties can be obtained, cure rates are quite slow as compared to a conventionally initiated acrylate system. The cost of using a cationic initiated system is often excessive.